This invention relates to an improved method for controlling the engine speed of an internal combustion engine, and is particularly, though not exclusively, useful in relation to water vehicles or watercraft and motorcycles or scooters.
Internal combustion engines are used in a wide variety of applications, such as in motor vehicles (cars, all terrain vehicles and two-wheeled vehicles) and watercraft including personal watercraft (PWCs) and outboard engines for boats. In many of these applications, it may be important in the operation of the engine to be able to govern or limit the rotational speed of the engine under certain circumstances.
For example, a requirement to limit engine speed may arise in order to protect an engine from damage which could be sustained during overly high speed operation, or to limit the overall speed of the vehicle or craft being powered by the engine. One such reason for limiting the speed of the engine may be to provide or enable a lower engine speed xe2x80x9climp-homexe2x80x9d mode of operation in response to certain information returned from a specific engine sensor or in response to a specific device failure. Such speed limiting or governing may also be desirable in instances where the operator of a vehicle or craft is inexperienced or if maximum speed limits are provided for a given situation.
PWCs represent one particular engine application where speed limiting may be desirable so as to control engine speed to a level lower than the normal maximum speed limit or capability of the engine. Such speed limiting may be particularly applicable where children or lesser experienced riders will be operating the PWC and additional safety is of concern. By way of such speed limiting, the rider will be unable to achieve the maximum speed of the engine or craft, this speed being likely to prove dangerous or unmanageable for the young or inexperienced rider. Accordingly, the rider""s safety is enhanced by restricting the maximum attainable speed of the engine or craft to one that is within the operational capabilities of the rider.
Such speed limiting may also be desirable for hire or rental organisations who may wish to preserve and prolong the usefulness of the products that they make available to the public by restricting the maximum attainable speed of an engine or craft. In this way, the craft is prevented from repeatedly operating at its upper or maximum limit and hence the longevity of the craft and engine thereof can be enhanced. This may be particularly desirable for engines which do not have a maximum speed control except for the engine""s natural maximum limit, leaving the engine particularly susceptible to damage from operation at overly high speeds.
Still further, certain legislative bodies are now regulating for lower maximum speeds in particular waterways and roads in built-up areas. Accordingly, the proliferation of such legislated speed limited zones is a further example of where it may be desirable to be able to limit the engine speed of a vehicle or craft.
In recent times, mechanical devices such as governors have been used, and developments in the electronic control of engines have resulted in a greater ability to govern or limit the speed of internal combustion engines. For example, in one such development, it has been proposed to prevent further increases in rotational speed once the engine has reached a preset limit by skipping combustion events. In such a method, typically, an ignition event is simply not scheduled for a particular engine cylinder, and a corresponding combustion event does not occur. This method however has the disadvantage that fuel is still delivered into the combustion chamber, and typically passes out through the engine exhaust system into the environment unburnt. This is both a significant waste of fuel and harmful to the environment. Additionally, residual unburnt fuel can remain in the combustion chamber and adversely affect the following combustion event by reducing the predictability and certainty with regard to the amount of fuel which will be combusted.
A further issue with certain existing speed governing systems is that the rider or operator is completely xe2x80x9cremoved from the loopxe2x80x9d during the period that the engine is operating under such speed governed conditions. That is, whilst the engine speed is being restricted to a certain predetermined limit, the operator effectively has little to no input in regard to the operation of the engine and a suitable controller determines what the specific engine event timings will be to maintain the speed at the preset level. Such operation may not be desirable in all situations and may have certain issues associated therewith.
For example, if the load on the engine was to increase whilst a speed limited mode was enabled, a typical controller would increase the fuelling rate to the engine in order to maintain the predetermined engine speed. However, this increase in fuelling would result without any regard to the operator. Further, such existing systems typically require the operator to specifically disengage the speed control means or to activate a separate deceleration means in order to regain operator control over the engine and in particular the throttle thereof. Such aspects which result from the driver or operator having the control of the engine removed from their authority hence introduces certain safety issues.
Accordingly, it is an object of the present invention to provide an engine speed control method which at least ameliorates some of the above problems. In particular, it is an object of the present invention to provide an engine speed control method wherein total engine control authority is not necessarily removed from the engine operator.
With the above object in mind, the present invention provides in one aspect a method of controlling the engine speed of an internal combustion engine, the method including the steps of determining the engine speed demanded by an operator of the engine and comparing this demanded engine speed with a predetermined engine speed limit, wherein if the demanded engine speed exceeds the predetermined engine speed limit, the fuelling rate demanded by the operator is only reduced in order to control the engine speed to the predetermined engine speed limit.
Conveniently, if the demanded engine speed is less than the predetermined engine speed limit, then no change is made to the normal operation of the engine. Accordingly, engine speed limited operation only occurs where the demanded engine speed exceeds the predetermined engine speed limit.
Preferably, where the demanded engine speed exceeds the predetermined engine speed limit, an engine speed control means is adapted to only reduce the amount of fuel demanded by an operator of the engine. Hence, even though the operator may demand a greater fuelling rate than that necessary to achieve the predetermined engine speed limit, during such speed limited operation, the actual fuelling rate to the engine never exceeds that corresponding to the predetermined engine speed limit. In effect, the controller which governs the fuelling rate to the engine functions in a unidirectional manner during speed limited engine operation to only ever reduce the demanded fuelling level.
Conveniently, the method as described above is used to control the engine speed to the predetermined speed limit with the level of reduction of the demanded fuelling rate, or the fuel sought to be delivered to the engine, being based on the demanded engine speed. Preferably, the actual amount of fuel to be delivered to the engine can be determined by considering the difference between the demanded engine speed and the engine speed limit and reducing the demanded or normal fuelling level accordingly. The normal fuelling level is considered to be the amount of fuel that would normally be injected, having regard to various parameters such as engine speed and throttle position, if a speed limit or target engine speed was not set and equates to the demanded engine speed.
Preferably, the amount of reduction to the demanded fuelling rate is directly controlled by the operator. That is, once speed limited operation has been enabled and no increase in engine speed is possible in response to further operation of a throttle means by the operator, such actuation of the throttle means may still serve as an input which assists determination of the reduction to the demanded fuelling rate. Hence, in determining the reduced fuelling level, regard may also be had to the position of the throttle means. Under normal operation, an increased throttle position would result in a greater amount of fuel being delivered into the combustion chamber. Accordingly, once the target speed has been reached, the amount of reduction required to the demanded fuelling rate will typically increase as the throttle position or degree of throttle opening increases. In this way, authority over the engine fuelling rate is not completely removed from the operator as the inputs made thereby via the throttle means are used to control the levels of reduction necessary to the demanded fuelling rate to maintain the predetermined limited engine speed.
In an alternative arrangement, throttle position input may be disregarded and rather than determining the required reduction in the fuelling level, a maximum or set amount of fuel may be delivered once the target speed has been reached. When the demanded engine speed subsequently falls below the target speed, normal fuelling levels may then be adopted.
Where the throttle position is varied by the operator during speed limited operation, the actual air-fuel ratio within the engine cylinders may vary due to increasing or decreasing degrees of throttle opening. That is, with a fixed fuelling level being delivered to the engine, throttle movement by the operator may result in a leaner or richer mixture being present in the engine cylinders. This may in turn have an undesirable effect on combustion stability and/or engine output torque. Accordingly, the timing and/or duration of certain engine events such as ignition and fuel delivery may no longer be ideal under such operating conditions.
In accordance with a further aspect of the present invention, there is provided a method of controlling the engine speed of an internal combustion engine including operating the engine in a speed limited mode in response to a demanded engine speed exceeding a predetermined engine speed limit, wherein modified event timings are used during said speed limited mode, said modified event timings varying from the normal event timings which would otherwise be used at the predetermined engine speed.
Preferably, when operating in said speed limited mode, the actual engine fuelling rate is that necessary to achieve the predetermined engine speed. Normal or a first set of event timings would typically be associated with this predetermined engine speed. The modified or second set of event timings relate to those timings which are preferably used when the air-fuel ratio to the engine varies from what it would typically be at the predetermined engine speed. As alluded to hereinbefore, this variance may be a consequence of the throttle position changing, even though the actual fuelling rate to the engine may remain the same.
Event timings typically relate to those key events during a combustion cycle which trigger the delivery and combustion of fuel for power generation in an engine. Ignition and the start and end of fuel delivery are examples of such key events. In a two-fluid fuel injection system, such events may further comprise separate start and end of air or delivery events (as distinct from start and end of metering or fuelling events).
In this regard, the present Applicant has designed and developed numerous such two-fluid fuel injection systems, one example of which is discussed in the Applicant""s U.S. Pat. No. 4,693,224, the contents of which are incorporated herein by reference. The method of operation of such a two-fluid fuel injection system typically involves the delivery of a metered quantity of fuel to each combustion chamber of an engine by way of a compressed gas, generally air, which entrains the fuel and delivers it from a delivery injector nozzle. Typically, a separate fuel metering injector, as shown for example in the Applicant""s U.S. Pat. No. RE36768, delivers, or begins to deliver, a metered quantity of fuel into a holding chamber within, or associated with, the delivery injector prior to the opening of the delivery injector to enable direct communication with a combustion chamber. When the delivery injector opens, the pressurised gas, or in a typical embodiment, air, flows through the holding chamber to entrain and deliver the fuel previously metered thereinto to the engine combustion chamber.
In an engine operated in accordance with such a two-fluid fuel injection strategy, there are therefore distinct events in the combustion process, including a fuel delivery event, an air delivery or injection event (as opposed to the bulk air delivery into the combustion chamber which occurs separately), and an ignition event. The engine management system typically required to implement such a strategy includes an electronic control unit which is able to independently control each of the fuel, air, and ignition events to effectively control the operation of the engine on the basis of operator input. As such, separate event timings typically exist for each of start of fuel metering (SOF), end of fuel metering (EOF), start of air injection (SOA), end of air injection (EOA) and ignition (IGN).
Conveniently, modified event timings may be used for at least one of SOF, EOF, SOA, EOA or IGN during the period that the engine is operating in speed limited mode. Such modified event timings are preferably selected so as to provide for an improved level of combustion stability and/or improved engine output torque during the speed limited mode and whilst the operator is varying the throttle position from that typically associated with the predetermined engine speed.
When operating in normal non-speed limited mode, the engine event timings may conveniently be selected from look-up maps which comprise total fuel per cycle (FPC) and engine speed as ordinates. This is typically true of a fuel-led engine control system where total FPC is essentially determined on the basis of throttle position and engine speed.
Preferably, when operating in speed limited mode, the modified engine event timings may be determined on the basis of total FPC and throttle position. Conveniently, total FPC and throttle position may be ordinates for an electronic lookup map or table which is stored in an electronic control unit (ECU) which manages the operation of the engine. Such ECUs are well known in the field of engine management and will not be elaborated on further herein. Alternatively, total FPC and air flow to the engine may be ordinates for the look-up table or map. In this manner, some allowance may also be made for engine operation at different attitudes. The adoption of either of the above alternatives is centred around the concept of replacing or eliminating the engine speed ordinate within the look-up in view of the fact that the engine speed is effectively held steady during the speed limited mode of operation. The event timings for the engine during such operation can hence more appropriately be determined on the basis of total FPC and either of throttle position or air flow (i.e. the new look-up table ordinates).
By providing modified event timings in this manner, the operator is still involved in determining which specific event timings are to be used by the ECU, even though the fuelling rate remains fixed for a given engine load.